Ground-penetrating radar investigation for the restoration of Al-Azhar historical minarets

Abstract

Ground-penetrating radar (GPR) is a modern geophysical tool that was developed for prospecting the ground subsurface. Recently, it has shown great potential for providing valuable information about the integrity of masonry structures. In this study, GPR was used to evaluate the state of bulk mason walls utilised as base foundation for the five historical minarets of Al-Azhar mosque in Cairo, Egypt constructed in different historical periods extending from Mamluk era to Ottoman era. The obtained results provided useful knowledge concerning the composition of the minaret bases and stones arrangement. Also, it showed the existence of multiple anomalies, indicating cavities that are probably caused by migration of fine filling materials downward. Limits of internal water content were clearly identified and salinity inside the wall filling was recognised. Based on these results, a decision was taken to re-inject the fine material lost through time inside the bases, to regain their structural integrity.